By means of MPU6, which is the control means, at the time of production, a reference voltage from an external device is applied to detector means 2 to be detected and converted to a digital signal in A/D converter means 3 and stored in memory means 4; while, at the time of operation, such as printing or image recording, the voltage of a battery equipped in the apparatus itself is applied to detector means 2 to be detected and converted to another digital value by the A/D converter means 3 to be applied to comparing means 5; the digital value of the reference voltage, already stored in memory means 4 is also applied to comparing means 5, and is compared with the battery voltage also stored in memory means 4, thereby it is determined whether the battery voltage will comply with the voltage which is necessary for performing the operation, such as printing operation, of the apparatus. In this process, it is possible to check the battery voltage of a battery-operated apparatus without involving any error.